Flake ice is made in thin sheets approximately 1.5-6.0 mm thick. The sheets may be curved or flat and the thin ice is generally broken into random-sized flakes when harvested.
Flake ice is particularly suitable for packing products such as fish or frozen foods as the ice flakes can be packed close to the products. In other applications such as chemical processing and concrete cooling, where rapid cooling is important, flake ice is ideal because the flakes present the maximum amount of cooling surface for a given amount of ice.
Flake ice is commonly produced by the application of water to the inside or outside of a refrigerated cylindrical drum. The water is applied at a first angular location on the drum and adheres thereto in a thin layer by surface tension. As the drum rotates, the water freezes into a thin layer of ice, which is fractured by an ice removal device at a second angular location downstream from the first angular location in the direction of rotation.
The thickness of the flake ice can be varied by adjusting the speed of the rotating drum, varying the evaporator temperature, and regulating the water flow on to the freezing surface. Since flake ice can be made in a continuous operation without being interrupted for a harvest cycle, less refrigeration tonnage is required to produce a tonne of ice than any other type of manufactured ice when similar make up water and evaporating temperatures are compared.
In known machines, water is applied to only one side of the drum, i.e., either the outside or inside, but not both. As a result, the refrigerated surface on the other side of the drum is unused, and the ice making operation represents an inefficient use of the refrigeration capacity of the machine.
Furthermore, as the ice removal device is located only on the side of the drum on which ice is formed, the continual unbalanced force applied to that side of the drum to fracture the ice from the freezing surface accelerates the wear on the drum bearings.
A further disadvantage of known ice making machines of the drum type is that their capacity cannot be readily increased. If increased capacity is desired, it is usually necessary to install a whole new machine. That is, in addition to installing an extra refrigerated drum, it is also necessary to install another refrigeration unit including motor, compressor and condenser, and a new drive unit. Any upgrading in capacity will therefore involve considerable expense.
U.S. Pat. No. 3,863,462 (Treuer) describes a machine for making flake ice by applying water to both sides of a rotating refrigerated disc. The water is applied by spray application and a thin layer of water adheres to the disc surfaces by surface adhesion. As the disc rotates, the water freezes to form a layer of ice, which is then dislodged from the disc surfaces by scraper blades or other means.
The flake ice machine of U.S. Pat. No. 3,863,462 has an upright refrigerated disc rotatable on a horizontal shaft. The disc is approximately 1.8m in diameter and comprises a pair of large round aluminum plates spaced apart about 20mm and sealed at their periphery to form an enclosed space. Baffles are placed within the interior of the disc to form rudimentary passages through which a chilled coolant is pumped. Due to the large flow passages inside the Treuer disc, it is necessary to use a non-evaporative or non-"boiling" refrigerant, such as brine or glycol.
As the coolant must remain liquid, it cannot be chilled below its freezing point, and hence its heat absorption capacity is limited. Due to the limited thermal capacity of the chilled coolant system, a relatively large amount of coolant must be pumped through the disc thereby requiring significant pumping capacity.
In addition, a separate refrigeration plant is required to chill the coolant before it is pumped through the disc. The Treuer machine therefore involves double heat transfer, namely first chilling the coolant, and then using the coolant to chill the surfaces of the disc. Inefficiencies and losses are introduced with each thermal transfer.
It is an object of the present invention to overcome or ameliorate at least some of the above-described disadvantages of the prior art by providing an improved ice making machine having at least one highly efficient rotatable, refrigerant disc configured internally to accommodate an evaporative refrigerant.
It is another object of the present invention to provide an improved refrigerated disc for use with the ice making machine.